How to hook up one LED light with two 6v sources?

I'm trying to hook up a tail/brake light on my moped and I'm wondering if its possible to use the one light for both brake and tail light. The light itself is a closed housing with two leads coming off the back, see the diagram as I'm probably not going to explain things all too well. The moped has three wires that originally powered two separate incandescent bulbs and the third wire being the ground completing the circuit. The brake light is only lit when I squeeze the brake lever where there is a switch that connects and sends the power back to the light.

Is there any way to connect these two wires into the one lead that could result in an increased brightness when I complete the brake lights circuit? My thinking is that I can put a resistor on the 'tail light (constantly fed)' lead and when the 'brake light' lead has power, the light will get the full 6v and become brighter. Am I close to being right about this? How can I keep the 'tail light' power from traveling through the 'brake light' wire? I know theres something I'm obviously missing here, its been a while since I've worked with voltage and maybe its not possible but I'm hoping theres a way.

Picture of How to hook up one LED light with two 6v sources?
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iceng5 years ago
The R1, R2 Values can be calculated when the LED is specified.

copalla (author)  iceng5 years ago
This is the light:



One site says 0.046 amps at 12.8v and the other 0.051 amps at 12.8v. I cant imagine that being to much a difference but I dont know.

The amps will matter for the resistor you will want to use. The problem is like i said... the LED in question wants 12.8V. The 6V provided by the tail light isn't enough to get the LED to light. It will only come on when you have the tail light on and the break on.
copalla (author)  mpilchfamily5 years ago
Are you saying that the voltages add together? I cant remember how that goes.
Your right i was a bit off. The 6V from the tail light and from the break light are not going to combine to give 12V. The way the original bulb works is it has 2 different filaments in it. One burns brighter then the other when 6V is applied. If you want LEDs for the tail light then you will need more then one or you will need some sort of controller that will run the LED. One that will keep the LED at a some what dimmed output and put the full power to the LED when the break is hit. Or run multiple LEDs so that only a few are light then when the break is hit it lights the rest of the LEDs. Or use 2 different LEDs that output a different amount of light. Either way the project is more complex then wiring a single LED to the 2 voltage sources.
iceng copalla5 years ago
Sorry, your moped is only 6 Volts and the lights are 12 Volts.

If you see anything it will be an unnoticeable glow.

PS there is no way that you get  12V by joining the two 6V lines.
copalla (author)  iceng5 years ago
I guess I'm not totally sure what the actual voltage is for the moped. I know I've had the light hooked up before and it did give me something but probably not enough to cut in half with a resistor and still get light.

What about a relay and battery set up? Just for the break light to get around 12v, or even 9v to light it up? I've attached a 9v battery to the light and that was plenty bright.
Short answer... NO.

First of all what LED do you plan to use? How much forward voltage and current does said LED draw?

If you connect the LEd to both inputs you will be going from 6V to 12V when the tail light is on and the break is pressed. If you are using some sort of LED or array of LEDs that use 12V then it won't even light is only one of the conditions (tail light on or break light on) is met. If you use some sort of LEd or array of LEDs that uses 6V then you will burn the LEDs out when both conditions are met and your pumping 12V to them.

Stick with the incandescent bulbs in vehicles. Unless you want to get complex about it and use more then 1 LED and a driver unit so the LEDs can be set dim for the tail light and full brightness when the break is on.